You're off to a great start by asking a question on this forum!
Since you've decided roughly when you want to go, you'll want to narrow down the exact dates for your trip next. From there, I would recommend choosing which resort hotel will work best for your family. There are rooms available in just about every price range, so begin by choosing which resort category you'd like to stay in: value, moderate, or deluxe. This handy
link might help you in researching that decision.
Since you mentioned the desire to enjoy a great pool, I'd be remiss if I didn't recommend Disney's Beach Club Resort. Stormalong Bay, the pool there, is absolutely fabulous! With a sandy bottom area and zero entry, it is great for children as young as yours. My family spent a few afternoons at the pool there during our most recent stay and each and every one of us completely enjoyed those relaxing afternoons poolside!
You know where to come when you have more planning questions!